The same echo time maps to a different depth when speed changes. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Sound speed also changes the depth scale
The echo time stays fixed; the scan changes only the training sound speed.
d=2ct
Three speeds give three exact depths for the same echo time
The same six-second echo is shallower or deeper only after the speed is cited.
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The middle speed gives the twelve-meter depth
The final equation uses the checked row that is also rendered.